1. Field of the Invention
This invention relates to an improved process for preparing the dye known as Acid Red 151 (Color Index No. 26,900) and to a non-gelling Acid Red 151.
2. Description of the Prior Art
Acid Red 151 is employed extensively in the dyeing of wool and synthetic fibers, especially nylon. The dye is commercially important because of its bright clear shade and good fastness properties.
Acid Red 151 is conventionally prepared by diazotizing aminoazobenzene monosulfonic acid in aqueous hydrochloric acid and reacting the diazotized amine with 2-naphthol in an aqueous sodium hydroxide solution. The dye prepared in this manner, however, when put in solution does not have good solubility and stability in high concentrations and exhibits gelling and specking properties.
The prior art relating to Acid Red 151 is directed primarily to methods for forming stable, concentrated solutions of the dye following synthesis of the dye according to conventional methods. Thus, for example, U.S. Pat. No. 3,957,425, teaches an improved aqueous organic solution of the salt of the disazo dye p-(p-(2-hydroxy-1-naphthylazo)phenylazo)benzenesulfonic acid.
It is an object of the present invention, therefore, to provide a method for the synthesis of Acid Red 151 that gives a dye which, when put in solution, has good solubility and forms non-gelling solutions that are stable over extended periods of time and when subjected to varying temperatures.
This and other objects will be apparent from the following description of the invention.